Figure 1. Modern pollen samples used in this study from the Neotoma Paleoecology Database.
Figure 2. The Southwest United States (SWUS) as defined here, showing locations of fossil pollen samples used in this study. Background shading indicates mean July temperature for 1961–1990 from PRISM (Daly et al. 2008; PRISM Climate Group 2019; Daly, Smith, and Olson 2015) at 800-m resolution. The solid gray box outlines the area studied by Bocinsky and Kohler (2014); the green dashed box shows the extent of the reconstruction in this study.
Figure 3. Temperature for the North Atlantic using Richard Alley’s (2000) Greenland ice core data (black line) and global mean surface temperature change (Osman et al. 2021) (using the 50th ensemble percentile) for 22,000 BC to present with the Younger Dryas and the general period of the northward expansion of maize agriculture from Mesoamerica into the SWUS highlighted.
Figure 4. Low-frequency component of the Moberg et al. (2005) multi-proxy reconstruction for Northern Hemisphere for AD 133–1925. PAGES2k reconstructed NH temperatures using different proxies that primarily shows high frequency resolution (PAGES 2k Consortium et al. 2019). Anomalies for both series are calculated in comparison to the 1961–1990 average.
Figure 5. Low-frequency bootstrapped summer temperature anomaly loess reconstruction from this study (blue) with standard error (gray) (top figure). Boxplots show estimates binned by century for all proxy samples (i.e., includes samples for the 100 simulations of the age-depth models). Anomalies are calculated in comparison to the 1961–1990 average. The temperature predictions using the median date from the age-depth model (i.e., does not include the 100 simulations) for each sample (not binned by century) are shown by circles; sizes of circles are inversely proportional to the sample-specific errors (size of circle ∝ 1/s1; see Simpson, 2007: 21 for calculation of s1). Anomaly estimates with larger circles are more precise. Histogram of proxy samples that includes the 100 simulations of the age-depth models through time in 100 year bins.
Figure 6. Low-frequency July temperature anomaly for the SWUS from this study, the North American July temperature reconstruction (André E. Viau et al. 2006) from 3000 BC to AD 2000, the terrestrial composite for 30–60 °N (Kaufman et al. 2020) from 3300 BC to AD 1700 in 500-year bins, and summer temperature for western North American (Routson et al. 2021). All series standardized to a mean of 0 and an s of 1 over the period in this graph (Routson et al. 2021 was already standardized).
Figure 7. Low-frequency July temperature anomaly for the SWUS from this study and the Northern Hemisphere low-frequency component (Moberg et al. 2005) from AD 133 to 1900. Pages2k reconstructed NH temperatures using different proxies that combine high and low frequency data (PAGES 2k Consortium et al. 2019). All series have been standardized to a mean of 0 and an s of 1 for this period.
| Site Name | Site ID | Dataset ID | No. of Samples | Elevation (m) | Longitude | Latitude |
|---|---|---|---|---|---|---|
| Alpine Pond | 9814 | 14517 | 26 | 3028 | -112.8245 | 37.63632 |
| Alpine Pond | 9814 | 14547 | 11 | 3028 | -112.8245 | 37.63632 |
| Bear Lake | 10000 | 14951 | 12 | 2752 | -112.1472 | 36.37112 |
| Beef Pasture | 246 | 250 | 90 | 3076 | -108.1604 | 37.47310 |
| Beef Pasture | 246 | 25551 | 71 | 3076 | -108.1604 | 37.47310 |
| Cascade Fen [Engineer Mountain Bog] | 339 | 347 | 63 | 2845 | -107.8087 | 37.64764 |
| Chihuahueños Bog | 13680 | 20833 | 18 | 2862 | -106.5105 | 36.04767 |
| Columbine Ranch Fen | 486 | 498 | 28 | 2793 | -107.8157 | 37.60664 |
| Como Lake | 2957 | 3056 | 9 | 3651 | -105.5142 | 37.56952 |
| Crane Lake | 504 | 517 | 7 | 2664 | -112.1489 | 36.52986 |
| Cumbres Bog | 11617 | 17419 | 30 | 3115 | -106.4505 | 37.02175 |
| Fracas Lake | 9997 | 14944 | 7 | 2530 | -112.2386 | 36.63070 |
| Hay Lake | 982 | 1013 | 5 | 2764 | -109.4250 | 34.00000 |
| Head Lake | 2955 | 3054 | 9 | 2295 | -105.7406 | 37.71109 |
| Hermit Lake | 23930 | 41580 | 26 | 3701 | -105.6317 | 38.08806 |
| Hospital Flat Meadow | 26738 | 46801 | 10 | 2875 | -109.8774 | 32.66757 |
| Hunters Lake | 13486 | 20304 | 20 | 3576 | -106.8437 | 37.61104 |
| Jacob Lake | 1127 | 1162 | 5 | 2326 | -110.8333 | 34.33333 |
| Leonora Curtin | 14632 | 22948 | 12 | 1867 | -106.1065 | 35.56948 |
| Lowder Creek Bog | 9830 | 14549 | 12 | 3186 | -112.7922 | 37.67214 |
| Molas Lake | 1705 | 1761 | 25 | 3282 | -107.6827 | 37.74759 |
| Molas Pass Bog | 1706 | 1762 | 15 | 3362 | -107.6975 | 37.73778 |
| Montezuma Well | 1710 | 1766 | 31 | 1112 | -111.7523 | 34.64920 |
| Posy Lake | 1905 | 1970 | 14 | 2693 | -111.6960 | 37.93746 |
| Potato Lake | 1906 | 3560 | 14 | 2280 | -111.3453 | 34.46222 |
| Potato Lake | 1906 | 3561 | 15 | 2280 | -111.3453 | 34.46222 |
| Purple Lake | 13683 | 20838 | 39 | 3321 | -111.5712 | 38.07438 |
| San Agustin Plains | 2260 | 3612 | 6 | 2115 | -108.2500 | 33.86667 |
| San Luis Lake | 9878 | 14650 | 24 | 2295 | -105.7247 | 37.67773 |
| Stewart Bog | 10191 | 15356 | 102 | 3083 | -105.7220 | 35.83200 |
| Stoneman Lake | 10449 | 15967 | 17 | 2132 | -111.5178 | 34.77887 |
| Twin Lakes | 2785 | 2880 | 54 | 3265 | -108.1026 | 37.46906 |
Supplemental Figure S1. Squared residual length for the fossil assemblages (including the 100 age-depth model simulations) vs age. Red line marks the 95% limit of the calibration set residual lengths (very poorly fitted). We removed all samples that fell above the 95% line.
Supplemental Figure S2. Summary diagram of the results of a MAT model applied to predict temperature from the modern pollen data set. The leave-one-out error measure (RMSEP) shows that 4 analogs provide the optimal choice (lowest RMSEP).
Supplemental Figure S3. ime series plot of the minimum dissimilarity between each core (fossil) sample (including the 100 simulations of the age-depth models) and the modern pollen training set samples. The dotted, horizontal lines are drawn at various percentiles of the distribution of the pair-wise dissimilarities for the training set samples. We used the 5th percentile as the cutoff for good analogs. So, samples with distances greater than the 5th percentile (above the line) were removed.
Supplemental Figure S4. Linear regression and scatterplot between temperature anomaly predicted values and the bootstrapped temperature predictions. There is a strong linear relationship across their joint ranges (r2 = 0.96; p > F < .001).
Supplemental Figure S5. Histogram of fossil pollen samples using the median date in 100 year bins.
Supplemental Figure S6. Low-frequency weighted bootstrapped temperature anomaly loess reconstruction from this study (blue) with standard error (gray). As in Figure 5 (main text) except here the loess curve (only) is weighted by the inverse of the sample-specific errors s1; see Simpson, 2007: 21 for calculation). CircleBubble size α 1/s1.
| Site Name | Site ID | Dataset ID | Anomaly (°C) | Anomaly Bootstrapped (°C) | Mean boostrap RMSEP (°C) | Mean boostrap s1 |
|---|---|---|---|---|---|---|
| Alpine Pond | 9814 | 14517 | 4.55 | 4.73 | 2.93 | 0.90 |
| Alpine Pond | 9814 | 14547 | 0.74 | 0.63 | 2.93 | 0.59 |
| Bear Lake | 10000 | 14951 | 9.59 | 7.61 | 3.22 | 2.30 |
| Beef Pasture | 246 | 250 | 11.77 | 10.93 | 4.66 | 2.28 |
| Beef Pasture | 246 | 25551 | 4.41 | 3.92 | 2.86 | 1.62 |
| Cascade Fen [Engineer Mountain Bog] | 339 | 347 | 4.86 | 4.50 | 3.09 | 1.09 |
| Chihuahueños Bog | 13680 | 20833 | 7.15 | 6.68 | 3.06 | 1.88 |
| Columbine Ranch Fen | 486 | 498 | 3.86 | 3.40 | 2.87 | 1.41 |
| Como Lake | 2957 | 3056 | 7.95 | 6.44 | 2.95 | 1.78 |
| Crane Lake | 504 | 517 | 5.00 | 2.63 | 2.81 | 1.84 |
| Cumbres Bog | 11617 | 17419 | 10.65 | 9.51 | 2.92 | 1.23 |
| Hay Lake | 982 | 1013 | 3.11 | 2.53 | 2.28 | 0.74 |
| Head Lake | 2955 | 3054 | 3.86 | 2.35 | 2.83 | 1.67 |
| Hermit Lake | 23930 | 41580 | 6.41 | 6.50 | 2.86 | 1.29 |
| Hospital Flat Meadow | 26738 | 46801 | 1.38 | 1.53 | 2.28 | 0.54 |
| Hunters Lake | 13486 | 20304 | 7.05 | 6.98 | 3.19 | 1.98 |
| Jacob Lake | 1127 | 1162 | 3.70 | 3.44 | 2.29 | 0.75 |
| Leonora Curtin | 14632 | 22948 | 4.14 | 3.30 | 2.75 | 1.48 |
| Lowder Creek Bog | 9830 | 14549 | 1.95 | 1.02 | 2.46 | 1.05 |
| Molas Lake | 1705 | 1761 | 5.29 | 4.61 | 2.55 | 0.98 |
| Molas Pass Bog | 1706 | 1762 | 2.11 | 1.64 | 2.93 | 1.81 |
| Montezuma Well | 1710 | 1766 | 3.35 | 2.82 | 2.79 | 1.32 |
| Posy Lake | 1905 | 1970 | 3.15 | 1.89 | 2.49 | 1.09 |
| Potato Lake | 1906 | 3560 | 3.18 | 2.95 | 2.95 | 1.47 |
| Potato Lake | 1906 | 3561 | 2.52 | 1.71 | 2.83 | 1.11 |
| Purple Lake | 13683 | 20838 | 2.38 | 1.53 | 2.49 | 0.62 |
| San Luis Lake | 9878 | 14650 | 5.66 | 4.96 | 2.90 | 1.84 |
| Stewart Bog | 10191 | 15356 | 9.60 | 9.84 | 4.18 | 1.26 |
| Stoneman Lake | 10449 | 15967 | 8.83 | 7.33 | 2.90 | 1.64 |
| Twin Lakes | 2785 | 2880 | 9.09 | 9.69 | 3.09 | 1.25 |
| Fracas Lake | 9997 | 14944 | NA | NA | NA | NA |
| San Agustin Plains | 2260 | 3612 | NA | NA | NA | NA |
| Year | Temperature Anomaly (°C) | Confidence Interval |
|---|---|---|
| -2950 | 0.4045296 | 1.1618605 |
| -2850 | 0.4414383 | 0.8050604 |
| -2750 | 0.4718849 | 0.6307377 |
| -2650 | 0.4881505 | 0.6074325 |
| -2550 | 0.4882839 | 0.6430761 |
| -2350 | 0.4696600 | 0.7031900 |
| -2250 | 0.3847865 | 0.6944113 |
| -2150 | 0.2431550 | 0.7145161 |
| -2050 | -0.0009257 | 0.6949540 |
| -1950 | -0.2118152 | 0.6957879 |
| -1850 | -0.3534270 | 0.6993471 |
| -1750 | -0.3573030 | 0.7294325 |
| -1650 | -0.1222834 | 0.7229518 |
| -1550 | 0.1342259 | 0.7133825 |
| -1450 | 0.3711475 | 0.7102845 |
| -1350 | 0.4147778 | 0.6993040 |
| -1250 | 0.1310486 | 0.6837305 |
| -1150 | -0.3198836 | 0.6631538 |
| -1050 | -0.6173994 | 0.6619437 |
| -950 | -0.5141464 | 0.6750019 |
| -850 | -0.0207968 | 0.6890323 |
| -750 | 0.4170984 | 0.7027943 |
| -650 | 0.5032538 | 0.7072723 |
| -550 | 0.3552907 | 0.7093661 |
| -450 | 0.2172818 | 0.6957468 |
| -350 | 0.2512441 | 0.6866448 |
| -150 | 0.3198603 | 0.6869330 |
| -50 | 0.3804943 | 0.7066400 |
| 50 | 0.2724975 | 0.6918105 |
| 150 | -0.0347638 | 0.7089141 |
| 250 | -0.4984228 | 0.6795270 |
| 350 | -0.7884595 | 0.6694945 |
| 450 | -0.6936688 | 0.6897010 |
| 550 | -0.3664989 | 0.6932318 |
| 650 | -0.1413861 | 0.7281681 |
| 750 | -0.1150580 | 0.7154483 |
| 850 | -0.2414175 | 0.7001981 |
| 950 | -0.5253352 | 0.6678101 |
| 1050 | -0.1924888 | 0.6897357 |
| 1150 | 0.2362539 | 0.7070884 |
| 1250 | 0.0836372 | 0.7147397 |
| 1350 | 0.0733919 | 0.6726624 |
| 1450 | -0.0210632 | 0.6557371 |
| 1550 | 0.0750696 | 0.6902302 |
| 1650 | 0.5968028 | 0.7251663 |
| 1750 | 0.8151299 | 0.7139425 |
| 1850 | 0.9663412 | 0.6594453 |
| 1950 | 1.4964440 | 0.8462535 |